1. Field of the Invention
The present invention relates to a waste liquid discharge system. More specifically, the present invention relates to a blockage alarm system for a waste liquid discharge machine which enables operators to have early knowledge of a blockage and thus have sufficient time to handle the situation.
2. Description of the Related Art
Photolithography is an important process for semiconductor fabrication. Every part of a semiconductor device such as patterns in the layers and regions implanted with dopants are formed using photolithography. Therefore, the number of lithography processes to be performed or the amount of masks required is a reflection of how difficult a fabrication process is.
Although the photolithography is complex, the basic principle thereof is simple. First, a layer of photosensitive material is applied on a surface of a die. The layer is radiated with parallel light from a light source through a mask mainly made of glass. The pattern on the mask is projected onto a surface of a die and selective development is performed, by which the pattern is transferred to the die. The photosensitive material on the surface of the die is called as a photoresist.
Currently, almost all of the photoresists are coated on the die by spin coating to obtain a photoresist having uniform thickness, high adhesion and no defects. Referring to FIG. 1, a schematic, cross-sectional view of rotator for spin coating and a conventional waste liquid discharge system are shown. The shift of the rotator 10 provides an appropriate vacuum to attach the wafer 12 thereon. When the rotator 10 rotates the wafer 12, the photoresist liquid 14 applied on the surface of the wafer 12 is moved toward the edge of the wafer 12 due to the action of the centrifugal force and finally a photoresist layer 16 having a uniform thickness is formed.
With high speed rotation of the rotator, some photoresist liquid 21 is spun off the wafer 12. Usually, a fixed container 20 is used to surround the wafer 12 to collect photoresist liquid spun off of the wafer 12, as shown in FIG. 1. The photoresist liquid 21 is transported to a discharge line 26 through the sides 22, 24 of the fixed container 20. Because the photoresist liquid is a liquid with high consistency, blockage often occurs in the non-vertical sections such as transversal transmitting part 28 in FIG. 1 when the discharge line 26 is not arranged in vertical direction. The photoresist may accumulate up to a level higher than the height of the machine and flow back on the machine. It is dangerous for the machine and operators because the above waste liquid may be a toxic waste liquid. If the toxic liquid is spilled, it takes time to evacuate people from the scene and perform post treatment.